In eletrophotographic applications such as xerography, an imaging surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the imaging surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a imaging surface operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during the transfer step, some toner invariably remains on the imaging surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the imaging surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom. Blade cleaning is a highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a imaging surface, because it provides a simple inexpensive structure compared to the various fiber or magnetic brush cleaners that are well known in the dry electrophotography art. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent and transversely across the imaging surface with a blade edge chiseling or wiping toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent the blade is transported away from the blade area by a toner transport arrangement or gravity. Unfortunately, blade cleaning suffers from certain deficiencies, primarily resulting from the frictional sealing contact which must be maintained between the blade and the imaging surface. Friction between the surfaces causes wearing away of the blade edge, and damaging wearing contact with the imaging surface. In addition to the problem of wear, which is more or less predictable over time, blades are also subject to unpredictable failures. The impact from carrier beads remaining on the imaging surface subsequent to development may damage the blade, and sudden localized increases in friction between the blade and surface may cause the phenomenon of tucking, where the blade cleaning edge becomes tucked underneath the blade, losing the frictional sealing relationship required for blade cleaning. These problems require removal and replacement of the blade.
It has been determined that at failure, streaks of toner and debris begin to occur, extending along the imaging surface in the process direction. Eventually, failure is noted by the user. It would be highly desirable to provide a sensor that detects cleaner failure, so that immediate corrective action may be taken by a machine subsystem to replace or rejuvenate the cleaner, or by service personnel notified remotely by a signal from the machine, or by an operator responding to a machine status message.
U.S. Pat. No. 4,705,388 to Huntjens et al. shows an arrangment for cleaning an imaging surface with a layer of tacky material that requires periodic rejuvenation. Light reflection from the tacky member is measured and compared with a standard to determine whether rejuvenation is required. U.S. Pat. No. 4,099,861 to Abel provides a monitor for the exhaust path of the cleaning apparatus, including light emitting diode (LED) downstream of the final filter and an optical sensor positioned to view the LED, which detects the concentration of particulate toner in the exhaust path. U.S. Pat. No. 4,046,471 to Branham et al. teaches a dual mode electrophotographic apparatus in which a laser is used both for formation of a latent image and to erase the borders around images when the device is used in light lens copying mode. U.S. Pat. No. 4,204,725 to DiStefano et al. teaches that a laser may be used for both formation of a latent image and for interrogation of a latent image on a surface to derive an electronic representation thereof. In the article, "A Method of Estimating Resistance to Abrasion", Journal of Applied Polymer Science, Vol. 14, pp. 1473-1475 (1970) by J. Bares, loss of reflectivity of a shiny surface is measured by decrease in specular surface reflectance.